Increased intakes of vitamin D are associated with a reduced risk of cardiovascular disease in men, but not women, suggest new findings from a Harvard-led study.

Men who met the Dietary Reference Intake of vitamin D of at least 600 IU per day had an associated risk of developing cardiovascular disease (CVD) that was 16 percent lower than men with a daily intake of less than 100 IU, according to findings published in the American Journal of Clinical Nutrition​.

“Unexpectedly”​, no such association was observed in women, which may be related to the doses, added researchers from Harvard School of Public Health (HSPH), the University of Massachusetts–Boston, Brigham and Women’s Hospital and Harvard Medical School.

“Because of the connection between sun exposure and skin cancer, avoidance of direct sun exposure and use of sun protection in outdoor activities have been recommended,”​ wrote the researchers, led by Qi Sun, a research associate in HSPH’s Department of Nutrition.

“Increasing vitamin D intake from foods or supplements, therefore, becomes one important measure to maintain optimal vitamin D status for persons who do not receive enough sun exposure. ​

“The current investigation provides the first evidence supporting potential benefits of moderate intake of vitamin D on CVD risk in men, whereas no associations were observed in women,”​ they added.

Shining light on the sunshine vitamin​

Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.

While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.

Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.

Men can take heart from the results​

The new study supports t he potential heart health benefits for men. The Boston-based scientists analyzed data from 74,272 women and 44,592 men, none of whom had CVD at the start of the study.

At the end of the study, 9,886 cases of coronary heart disease and stroke were documented. A 16 percent reduction was observed for men who met the DRI, compared to men with daily intakes of less than 100 IU, but no such benefits were observed in women.

Explanations? ​

Commenting on the potential mechanism, the researchers said that vitamin D may influence the reninangiotensin system (linked to blood pressure regulatio), function of the endothelium (the cells lining blood vessels), insulin resistance, and systemic inflammation. “These mechanisms may explain the inverse association between vitamin D intake and CVD risk in men,”​ they said.

For the women, however, the researchers said the result was “unexpected”​ but consistent with previous studies, and this is perhaps linked to a low dose of vitamin D being used.

“Additional studies are warranted before a firm conclusion regarding the effects of vitamin D intake or supplements on CVD outcomes can be made,”​ they said.

“Nonetheless, a large trial that examines the effects of high-dose vitamin D supplementation (2000 IU/d) on the primary prevention of CVD, cancer, and other chronic diseases is being conducted.”​

Irony​

Commenting on the results, Harry Rice, PhD, VP of scientific and regulatory affairs at the United Natural Products Alliance (UNPA) said that the study suggests that the recently announced recommended dietary allowance (RDA) of 600 IU of vitamin D may also provide cardiovascular, in addition to bone health, benefits.

“It will be ironic if this level is corroborated by results from future investigations given that the IOM Dietary Reference Intake (DRI) Review Committee indicated that ‘with the exception of measures related to bone health, the potential indicators examined are currently not supported by evidence that could be judged either convincing or adequate in terms of cause and effect, or informative regarding dose–response relationships for determining nutrient requirements’,”​ said Dr Rice.

“The finding that total vitamin D, especially vitamin D from supplements, but not from the diet, was inversely associated with cardiovascular disease risk is supportive of the idea that people aren’t obtaining sufficient quantities of vitamin D through diet alone,”​ he added.

1 comment

2000 IU Still a Low Dose!

Posted by Richard C. Snouffer, MD,
06 July 2011 - 13:28 GMT

I am a physician practicing in the Southern USA. (Alabama) I measure Vitamin D, 25-OH levels on ALL my patients. In my personal professional experience, I have YET to see any adult get into the optimal range of this Vitamin D metabolite (60-100) on less than 2,000 IU daily, and MOST of my patients require between 5,000-10,000 IU to become therapeutic.

Of course, a physician should be consulted and lab levels checked and patient history reviewed prior to initiating such "high" levels of therapy. However, this experience in the SOUTHERN USA makes me think that the USRDA of 600 IU daily is ridiculously inadequate!